Bill Ruckelshaus knows White House skulduggery when he sees it. A former deputy attorney general who is the last prominent survivor among the Watergate investigators who brought down President Richard Nixon, Ruckelshaus has some advice for President Donald Trump.

"There is only one person that could shut down all the current speculation and that is Trump," he said the other day in an email from Seattle, where he practices law. "If he would turn over all the information he has and instruct his minions to do the same, and there is no incriminating evidence involving him, the speculation would end."

Oh, and one other thing: Don't even think about firing Robert Mueller, the special counsel looking into Trump connections to Russia and related matters.

Ruckelshaus resigned from Nixon's Justice Department in 1973 after refusing to follow the president's order to fire special counsel Archibald Cox, who was leading the Watergate probe. That happened hours after the departure for the same reason of Attorney General Elliott Richardson.

Ruckelshaus, now 84, also had been an acting director of the Federal Bureau of Investigation when it was conducting the early inquiry into the break-in by a team of Republican operatives at the Democratic Party headquarters in the Watergate complex near the White House. He has an acute sense of how these matters evolve.

In the current scandal, he notes that Trump "after all, says he has done nothing wrong." If that's true, Ruckelshaus says, it's a good reason to release everything that might be relevant to the investigation.

"There is a time limit on his ability to do this," Ruckelshaus warned, "and it is rapidly approaching."

Harking back to his earlier experience, he recalls: "Nixon could have done the same thing if he had acted immediately upon learning of the Watergate break-in in June of 1972. Instead he led the coverup."

Ruckelshaus, a Republican then and now, warns that Trump "will be in real trouble" if he tries to remove Mueller. "The dismissal of Cox in October of 1973 led to the Rodino Committee (the House Impeachment Committee) and then ultimately the resignation of Nixon in August of 1974," he wrote.

Ruckelshaus was appointed to four top posts by Nixon. In addition to the Justice Department jobs, he was the first administrator of the Environmental Protection Agency, where he was widely praised for creating an effective new agency. He had an unsurpassed reputation for integrity. He was considered as President Gerald Ford's running mate in 1976; some Ford strategists still think that if he had been chosen, rather than Senator Bob Dole, the Republicans could have won the presidential election that year.

If Trump respects experience, you'd expect him to heed this Watergate hero's advice. Ruckelshaus says he isn't holding his breath:

"I do not personally believe," he wrote, that "Trump is capable of taking the approach I am suggesting, any more than was Nixon."

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Albert R. Hunt is a Bloomberg Opinion columnist covering politics and policy. He was the executive editor of Bloomberg News, before which he was a reporter, bureau chief and executive Washington editor at the Wall Street Journal.